
Use of conserved quantities. Equation (REF ) has the conserved quantity (REF ). Likewise the \(b-\) equation, it implies the conservation of the \(L^1(X)-\) norm of a solution \(u\)  of (REF ) as long as \(u\)  is either non-negative or non-positive. Proceeding similarly as for the \(b-\) equation, we conclude that \(u\equiv 0\) .

Use of data-to-solution map. The FW equation is locally well-posed, see [1]}, [2]}. The result follows the same steps as for the \(b-\) equation and for this reason is omitted.

